making ampeg b3 louder

Hi, The last few days I've been asking some questions reagarding my current amp- USA made Ampeg B3, 4 ohms, 150W, 115"- and I've really appreciated the input. I know very little about amps, OHMS, wattage, etc and have been reading lots of info, though since there is so many opinions out there, it's hard to grasp it all.
Question: Can I make this amp louder? Can I hook up another cab to it to do so? Would the B3 be enough if I just run it through the PA? I'd rather not spend the $ to upgrade if I don't need to. I'd be using the amp for bar gigs, BBQs and these types of events, if that helps...

[JimmyM]

if you run through the pa, it should be fine. and if your band isn't super loud, it should also be fine. unfortunately, a lot of the reason those b series combos are cheap is because they're not really upgradeable. most have no ext speaker out, and as on your amp, most are already running at 4 ohms, which is as much power as you're going to get, and even if you can run a second speaker, the wattage will get cut so the gains won't be as big. short of scrapping the cab and putting the head on a bigger cab with more speakers, you're getting about all you can out of it.

JimmyM- Thank you for that informative post that pretty much told me all I need to know. I think what I will do is use the B3, mic it through the PA, and upgrade if the need arises. Meanwhile, I'll keep reading up on what's out there and see if anything good comes around on Craigslist. Thanks again.